The overall goal of this HIVRAD consortium is to develop and compare four novel vaccine candidates designed to deliver HIV envelope (Env) trimers mimicking the presentation of Env by HIV infection and ultimately generating broadly neutralizing antibodies (bNAbs) against the AIDS virus. The team will work towards this goal by completing objectives in four Specific Aims. Aim 1 intends to design, develop, and characterize vaccine candidates that deliver stabilized, membrane-anchored Clade C 1086 spikes adapted from the well-ordered native flexibly linked (NFL) trimer design (EnvNFL). Aim 2 will conduct initial immunogenicity studies comparing the candidates in inbred mice including analysis of gene expression profiles, cellular and humoral immune responses, and Env-specific antibodies and B-cells guiding iterative improvement of the candidates. Aim 3 will further test the optimized candidates in small animal models that enable evaluation of HIV-neutralization activity elicited by vaccination including rabbits and novel, genetically-modified mice (VelocImmune(r)) that express antibodies with human VH and Vk domains. Aim 4 will prioritize two vaccine regimens for evaluation in macaques based on accumulated comparative data from small animal studies in Aims 2 and 3, ultimately conducting mucosal SHIV challenge experiments to correlate vaccine performance with degree of resistance to SHIV infection. Compared to previous HIV vaccine trials, this program hypothesizes that performance gains can be achieved if an Env vaccine is designed to deliver authentic spikes arrayed on enveloped particles, and if a trimer delivery platform can be identified that provides immunostimulatory signals promoting polyclonal responses of greater epitope breadth encompassing Abs with bNAb specificities. To this end, four novel Env trimer vaccines based on different delivery technologies that will evoke unique immune response profiles will be developed and compared. Each vaccine will deliver clade C trimers based on the EnvNFL design to promote efficient assembly of well-ordered complexes of greater uniformity and increased stability. The four vaccine platforms are: 1) RNActive(r) technology, an innovative mRNA vector and adjuvant delivery system; 2) EnvNFL trimers assembled on liposome-based VLPs; 3) EnvNFL trimers displayed on inactivated vesicular stomatitis virus (VSV) particles; and 4) EnvNFL delivered with a live VSV vector that incorporates Env in its viral envelope. Three projects supported by three cores will undertake the above experimental plan. Project 1 will design and develop the vectors in concert with Project 2, which will provide the Env trimers and develop a liposome-based vaccine, while Project 3 will evaluate the HIV Env-specific B cell repertoire in the small animal and NHP studies. Core C will provide gene signature analysis of the vaccine platforms and Core B will carry out the small animal and NHP studies. Administrative Core A will provide overall management of the program. Overall, the program will develop four new Env vaccines delivering stabilized trimers, and generate a comprehensive database on their performance in multiple animal models including nonhuman primates.